Paul O. Collinson

Analytical characteristics of high-sensitivity cardiac troponin assays.

BACKGROUND Cardiac troponins I (cTnI) and T (cTnT) have received international endorsement as the standard biomarkers for detection of myocardial injury, for risk stratification in patients suspected of acute coronary syndrome, and for the diagnosis of myocardial infarction. An evidence-based clinical database is growing rapidly for high-sensitivity (hs) troponin assays. Thus, clarifications of the analytical principles for the immunoassays used in clinical practice are important. CONTENT The purpose of this mini-review is (a) to provide a background for the biochemistry of cTnT and cTnI and (b) to address the following analytical questions for both hs cTnI and cTnT assays: (i) How does an assay become designated hs? (ii) How does one realistically define healthy (normal) reference populations for determining the 99th percentile? (iii) What is the usual biological variation of these analytes? (iv) What assay imprecision characteristics are acceptable? (v) Will standardization of cardiac troponin assays be attainable? SUMMARY This review raises important points regarding cTnI and cTnT assays and their reference limits and specifically addresses hs assays used to measure low concentrations (nanograms per liter or picograms per milliliter). Recommendations are made to help clarify the nomenclature. The review also identifies further challenges for the evolving science of cardiac troponin measurement. It is hoped that with the introduction of these concepts, both laboratorians and clinicians can develop a more unified view of how these assays are used worldwide in clinical practice.

Role of "Ischemia modified albumin", a new biochemical marker of myocardial ischaemia, in the early diagnosis of acute coronary syndromes.

Background: Diagnosis of cardiac ischaemia in patients attending emergency departments (ED) with symptoms of acute coronary syndromes is often difficult. Cardiac troponin (cTn) is sensitive and specific for the detection of myocardial damage but may not rise during reversible myocardial ischaemia. Ischemia Modified Albumin (IMA) has recently been shown to be a sensitive and early biochemical marker of ischaemia. Methods and Results: This study evaluated IMA in conjunction with ECG and cTn in 208 patients presenting to the ED within three hours of acute chest pain. At presentation, a 12-lead ECG was recorded and blood taken for IMA and cardiac troponin T (cTnT). Patients underwent standardised triage, diagnostic procedures, and treatment. Results of IMA, ECG, and cTnT, alone and in combination, were correlated with final diagnoses of non-ischaemic chest pain, unstable angina, ST segment elevation, and non-ST segment elevation myocardial infarction. In the whole patient group, sensitivity of IMA at presentation for an ischaemic origin of chest pain was 82%, compared with 45% of ECG and 20% of cTnT. IMA used together with cTnT or ECG, had a sensitivity of 90% and 92%, respectively. All three tests combined identified 95% of patients whose chest pain was attributable to ischaemic heart disease. In patients with unstable angina, sensitivity of IMA used alone was equivalent to that of IMA and ECG combined. Conclusions: IMA is highly sensitive for the diagnosis of myocardial ischaemia in patients presenting with symptoms of acute chest pain.

Ischemia Modified Albumin Is a Sensitive Marker of Myocardial Ischemia After Percutaneous Coronary Intervention

Background—Ischemia modified albumin (IMA; Ischemia Technologies, Inc) blood levels rise in patients who develop ischemia during percutaneous coronary intervention (PCI). It is not known whether IMA elevations correlate with increases in other markers of oxidative stress, ie, 8-iso prostaglandin F2-A (iP). Methods and Results—We compared IMA versus iP plasma levels in 19 patients (mean age 62.8±11.9 years) undergoing PCI and 11 patients (mean age 64±13.6 years) undergoing diagnostic angiography (controls). In the PCI patients, blood samples for IMA and iP were taken from the guide catheter before PCI and after balloon inflations, and from the femoral sheath 30 minutes after PCI. IMA was measured by the albumin cobalt binding (ACB) test and plasma iP by enzyme immunoassay. During PCI, all 19 patients had chest pain and 18 had transient ischemic ST segment changes. IMA was elevated from baseline in 18 of the 19 patients after PCI. Median IMA levels were higher after PCI (101.4 U/mL, 95%CI 82 to 116) compared with baseline (72.8 U/mL, CI 55 to 93;P <0.0001). Levels remained elevated at 30 minutes (87.9 U/mL, CI 78 to 99;P <0.0001) and returned to baseline at 12 hours (70.3 U/mL, CI 65 to 87;P =0.65). iP levels were raised after PCI in 9 of the 19 patients. However, median iP levels were not significantly different immediately (P =0.6) or 30 minutes after PCI (P =0.1). In the control group, IMA and iP levels remained unchanged before and after angiography (P =0.2 and 0.16, respectively). Conclusions—IMA is a more consistent marker of ischemia than iP in patients who develop chest pain and ST segment changes during PCI.

Prospective study of the role of cardiac troponin T in patients admitted with unstable angina

Abstract Objective: To examine the prognostic significance and role in risk stratification of the biochemical marker troponin T in patients admitted with unstable angina. Design: Single centre, blinded, prospective study of patients admitted with chest pain. Setting: Coronary care unit of a district general hospital. Subjects: 460 patients admitted with chest pain and followed up for a median of three years. 183 patients had a final diagnosis of unstable angina. Main outcome measures: Cardiac death, need for coronary revascularisation, or readmission with non-fatal myocardial infarction as first events. Results: 62 (34%) unstable angina patients were troponin T positive. This group had significantly increased incidence rates of subsequent cardiac death (12 cases (19%) v 14 (12%)), coronary revascularisation (22 (35%) v 26 (21%)), death or revascularisation (33 (53%) v 40 (33%)), and death or non-fatal myocardial infarction (18 (29%) v 21 (17%)) compared with the troponin T negative group. In multiple logistic regression troponin T status was a highly significant predictor for the end points coronary revascularisation and cardiac death or revascularisation as first events. Conclusion: Troponin T in the serum of patients with unstable angina identifies a subgroup at higher risk of subsequent cardiac events and its measurement aids in risk factor stratification. The increased risk extends to two years after admission. Prospective randomised trials are required to identify optimum therapeutic strategies for this subgroup. Key messages Stratifying patients with unstable angina for risk remains a difficult clinical problem A new cardiac specific protein, troponin T, can now be measured in serum The detection of troponin T 12-24 hours after admission identifies a high risk subgroup of patients with unstable angina Prospective trials are required to identify optimum therapeutic strategies for this subgroup

High sensitivity cardiac troponin and the under-diagnosis of myocardial infarction in women: prospective cohort study.

Objective To evaluate the diagnosis of myocardial infarction using a high sensitivity troponin I assay and sex specific diagnostic thresholds in men and women with suspected acute coronary syndrome. Design Prospective cohort study. Setting Regional cardiac centre, United Kingdom. Participants Consecutive patients with suspected acute coronary syndrome (n=1126, 46% women). Two cardiologists independently adjudicated the diagnosis of myocardial infarction by using a high sensitivity troponin I assay with sex specific diagnostic thresholds (men 34 ng/L, women 16 ng/L) and compared with current practice where a contemporary assay (50 ng/L, single threshold) was used to guide care. Main outcome measure Diagnosis of myocardial infarction. Results The high sensitivity troponin I assay noticeably increased the diagnosis of myocardial infarction in women (from 11% to 22%; P<0.001) but had a minimal effect in men (from 19% to 21%, P=0.002). Women were less likely than men to be referred to a cardiologist or undergo coronary revascularisation (P<0.05 for both). At 12 months, women with undisclosed increases in troponin concentration (17-49 ng/L) and those with myocardial infarction (≥50 ng/L) had the highest rate of death or reinfarction compared with women without (≤16 ng/L) myocardial infarction (25%, 24%, and 4%, respectively; P<0.001). Conclusions Although having little effect in men, a high sensitivity troponin assay with sex specific diagnostic thresholds may double the diagnosis of myocardial infarction in women and identify those at high risk of reinfarction and death. Whether use of sex specific diagnostic thresholds will improve outcomes and tackle inequalities in the treatment of women with suspected acute coronary syndrome requires urgent attention.

High-sensitivity cardiac troponin I at presentation in patients with suspected acute coronary syndrome: a cohort study

Summary Background Suspected acute coronary syndrome is the commonest reason for emergency admission to hospital and is a large burden on health-care resources. Strategies to identify low-risk patients suitable for immediate discharge would have major benefits. Methods We did a prospective cohort study of 6304 consecutively enrolled patients with suspected acute coronary syndrome presenting to four secondary and tertiary care hospitals in Scotland. We measured plasma troponin concentrations at presentation using a high-sensitivity cardiac troponin I assay. In derivation and validation cohorts, we evaluated the negative predictive value of a range of troponin concentrations for the primary outcome of index myocardial infarction, or subsequent myocardial infarction or cardiac death at 30 days. This trial is registered with ClinicalTrials.gov (number NCT01852123). Findings 782 (16%) of 4870 patients in the derivation cohort had index myocardial infarction, with a further 32 (1%) re-presenting with myocardial infarction and 75 (2%) cardiac deaths at 30 days. In patients without myocardial infarction at presentation, troponin concentrations were less than 5 ng/L in 2311 (61%) of 3799 patients, with a negative predictive value of 99·6% (95% CI 99·3–99·8) for the primary outcome. The negative predictive value was consistent across groups stratified by age, sex, risk factors, and previous cardiovascular disease. In two independent validation cohorts, troponin concentrations were less than 5 ng/L in 594 (56%) of 1061 patients, with an overall negative predictive value of 99·4% (98·8–99·9). At 1 year, these patients had a lower risk of myocardial infarction and cardiac death than did those with a troponin concentration of 5 ng/L or more (0·6% vs 3·3%; adjusted hazard ratio 0·41, 95% CI 0·21–0·80; p<0·0001). Interpretation Low plasma troponin concentrations identify two-thirds of patients at very low risk of cardiac events who could be discharged from hospital. Implementation of this approach could substantially reduce hospital admissions and have major benefits for both patients and health-care providers. Funding British Heart Foundation and Chief Scientist Office (Scotland).

Plasma DNA concentration as a predictor of mortality and sepsis in critically ill patients

IntroductionRisk stratification of severely ill patients remains problematic, resulting in increased interest in potential circulating markers, such as cytokines, procalcitonin and brain natriuretic peptide. Recent reports have indicated the usefulness of plasma DNA as a prognostic marker in various disease states such as trauma, myocardial infarction and stroke. The present study assesses the significance of raised levels of plasma DNA on admission to the intensive care unit (ICU) in terms of its ability to predict disease severity or prognosis.MethodsFifty-two consecutive patients were studied in a general ICU. Blood samples were taken on admission and were stored for further analysis. Plasma DNA levels were estimated by a PCR method using primers for the human β-haemoglobin gene.ResultsSixteen of the 52 patients investigated died within 3 months of sampling. Nineteen of the 52 patients developed either severe sepsis or septic shock. Plasma DNA was higher in ICU patients than in healthy controls and was also higher in patients who developed sepsis (192 (65–362) ng/ml versus 74 (46–156) ng/ml, P = 0.03) or who subsequently died either in the ICU (321 (185–430) ng/ml versus 71 (46–113) ng/ml, P < 0.001) or in hospital (260 (151–380) ng/ml versus 68 (47–103) ng/ml, P < 0.001). Plasma DNA concentrations were found to be significantly higher in patients who died in the ICU. Multiple logistic regression analysis determined plasma DNA to be an independent predictor of mortality (odds ratio, 1.002 (95% confidence interval, 1.0–1.004), P = 0.05). Plasma DNA had a sensitivity of 92% and a specificity of 80% when a concentration higher than 127 ng/ml was taken as a predictor for death on the ICU.ConclusionPlasma DNA may be a useful prognostic marker of mortality and sepsis in intensive care patients.

Influence of Population Selection on the 99th Percentile Reference Value for Cardiac Troponin Assays

OBJECTIVE We sought to determine the effect of patient selection on the 99th reference percentile of 2 sensitive and 1 high-sensitivity (hs) cardiac troponin assays in a well-defined reference population. METHODS Individuals>45 years old were randomly selected from 7 representative local community practices. Detailed information regarding the participants was collected via questionnaires. The healthy reference population was defined as individuals who had no history of vascular disease, hypertension, or heavy alcohol intake; were not receiving cardiac medication; and had blood pressure<140/90 mmHg, fasting blood glucose<110 mg/dL (approximately 6 mmol/L), estimated creatinine clearance>60 mL·min(-1)·(1.73 m2)(-1), and normal cardiac function according to results of echocardiography. Samples were stored at -70 °C until analysis for cardiac troponin I (cTnI) and cardiac troponin T (cTnT) and N-terminal pro-B-type natriuretic peptide. RESULTS Application of progressively more stringent population selection strategies to the initial baseline population of 545 participants until the only individuals who remained were completely healthy according to the study criteria reduced the number of outliers seen and led to a progressive decrease in the 99th-percentile value obtained for the Roche hs-cTnT assay and the sensitive Beckman cTnI assay but not for the sensitive Siemens Ultra cTnI assay. Furthermore, a sex difference found in the baseline population for the hs-cTnT (P=0.0018) and Beckman cTnI assays (P<0.0001) progressively decreased with more stringent population selection criteria. CONCLUSIONS The reference population selection strategy significantly influenced the 99th percentile reference values determined for troponin assays and the observed sex differences in troponin concentrations.

Analytical performance of the N terminal pro B type natriuretic peptide (NT-proBNP) assay on the Elecsys™ 1010 and 2010 analysers

The Elecsys NT‐proBNP assay is based on two polyclonal antibodies directed at residues 1–21 and 39–50 of the NT‐proBNP molecule. Analytical performance was assessed using NCCLS protocol EP‐5A using three serum pools in a preliminary study then as part of a multicentre evaluation (16 instruments in 8 hospitals). Using pools of 350 pg/l, 8700 pg/l and 13000 pg/l single site within run %CV was 0.7–1.6 (1010) and 1.2–1.5 (2010) and between run CV 5.3–6.7 (1010) and 4.4–5.0 (2010). In the multicentre evaluation within run CV was 1.0–2.5% with total imprecision 1.5–2.5% and between labs imprecision 3.8–4.0%. Functional sensitivity of <50 pg/l and measuring range to 35000 pg/l. There was excellent agreement between instrument platforms, y=0.97x+2.6; r=1.00 (n=215) for Elecsys 2010 (x) vs. Elecsys 1010 (y) and y=1.02x−0.3; r=1.00 (n=99) for Elecsys 2010 (x) vs. E 170 (y). Serum and heparin plasma samples showed good agreement but lower values were seen in EDTA plasma. Samples were stable for 7 days at room temperature; 21 days at 4 °C and for 5 freeze thaw cycles. Samples were obtained from a population of 1205 (671 male, 534 female) apparently healthy individuals screened by echocardiography and symptom questionnaire. There was poor correlation with NT‐proANP (ELISA) (rs 0.33) and modest correlation with BNP (rs 0.89) with NT‐proBNP values approximately 5 times greater than BNP (Biosite Triage). In a subset of 320 with normal ejection fraction (>50%) and no risk factors, NT‐proBNP values increased with age and were higher in women than men.

Cardiac Troponin T Release Is Stimulated by Endurance Exercise in Healthy Humans

To the Editor: Post-exercise release of cardiac troponin (cTn)T and cTnI has been previously reported after prolonged bouts of exercise ([1][1]). However, this release has only been observed in a limited number of subjects ([2][2]). It is unclear whether post-exercise release of cTn represents